The subject invention relates to polymers made by anionic initiation with alkyllithium compounds containing cyclic amines, such as polymerizations of dienes and diene/comonomer mixtures resulting in diene polymer and copolymer elastomers. Polymers prepared with the compounds of the present invention exhibit improved characteristics such as for example, improved hysteresis loss characteristics, and reproducible, relatively narrow range molecular weight distributions.
When conducting polymerizations on a commercial basis, it is important to utilize process conditions and components which will allow the molecular weight of the end products to be narrowly and reproducibly defined. The characteristics of a given polymer and its usefulness, are dependent, among other things, upon its molecular weight. Hence, it is desirable to be able to predict with some certainty the molecular weight of the end product of the polymerization. When the molecular weight is not narrowly definable, or is not reproducible on a systematic basis, the process is at a commercial disadvantage.
Further, it is desirable to produce elastomeric compounds exhibiting improved characteristics such as reduced hysteresis loss characteristics. Such elastomers, when compounded to form articles such as tires, power belts and the like, will show an increase in rebound, a decrease in rolling resistance and less heat build-up when mechanical stresses are applied.
A major source of hysteretic power loss has been established to be due to the section of the polymer chain from the last cross link of the vulcanizate to the end of the polymer chain. This free end cannot be involved in an efficient elastic recovery process, and as a result, any energy transmitted to this section of the cured sample is lost as heat. It is known in the art that this type of mechanism can be reduced by preparing higher molecular weight polymers which will have fewer end groups. However, this procedure is not useful because processability of the rubber with compounding ingredients and during shaping operations decreases rapidly with increasing molecular weight of the rubber.
The present invention provides polymers made by anionic initiation with novel alkyl lithium compounds containing cyclic amines. Use of the compounds of the present invention allows the incorporation of a functionality from the initiator to be incorporated at least at the head of the polymer chain. The initiators used in the invention not only provide for improved polymerizations, but also result in polymers having a relatively predictable, controllable and reproducible molecular weight range distribution. Because of the incorporated functionality, the polymers and products of the invention exhibit improved (that is, reduced) hysteresis loss characteristics.
Certain aminoalkyllithium compounds are known in the art. For example, U.S. Pat. No. 4,935,471 discloses dialkylamino oligoalkenyl lithiums including piperidinyl and pyrrolidinyl oligoalkenyl lithiums. It has been found that when compounded with conventional vulcanizable rubber components, some of these materials do not interact effectively with carbon black. Others possess an odor which makes their commercial use undesirable. The present invention provides polymers derived from aminoalkyllithium compounds with improved interaction with carbon black and which do not have the objectionable odor associated with the piperidinyl and pyrrolidinyl compounds.
It is therefore, an object of the present invention to provide polymers formed by anionic polymerization initiators.
It is a further object of the invention to provide a polymerization initiator which using such to initiate a polymerization will reproducibly result in a polymer within a narrow, predictable molecular weight range.
It is an additional object of the invention to provide a polymerization initiator which using such to initiate a polymerization will allow for the incorporation of a functional group at both the head and tail of the resulting polymer.
It is another object of the present invention to provide elastomers formed with such a polymerization initiator.
It is yet another object of the present invention to provide elastomers having a plurality of polymer molecules wherein substantially each molecule has a functional group from the initiator.
It is also an object of certain embodiments of the present invention to provide diene polymers and copolymers having reduced hysteresis characteristics.
It is a further object of the present invention to provide vulcanizable elastomeric compounds.
Still another object of the present invention is to provide an improved tire formed from an elastomer as described hereinabove.
At least one or more of these objects together with the advantages thereof over the existing art, which shall become apparent from the specification which follows, are accomplished by the invention as hereinafter described and claimed.
In general, according to the invention, a functionalized polymer comprises a polymer molecule having the general formula AYLi where A is a cyclic amine-containing radical having the general formula (I) 
wherein R1 and R2 are as discussed hereinabove; and Y is a divalent polymer radical.
A functionalized polymer according to the present invention also comprises a polymer molecule having the general formula AYLi where A is a cyclic amine-containing radical having the general formula 
wherein A, R2, R5 and Y are as discussed hereinabove.
There is also provided according to the invention a method of preparing a polymer which comprises preparing a solution of 1 or more anionically polymerizable monomers in a solvent; and, polymerizing under effective conditions, the monomers in the presence of a polymerization initiator having the general formula 
wherein R1 and R2 are as discussed hereinabove.
A method for preparing a polymer according to the present invention comprises preparing a solution of 1 or more anionically polymerizable monomers in a solvent; and polymerizing under affective conditions, the monomers in the presence of a polymerization initiator having the general formula 
wherein R2 and R5 are as discussed hereinabove.
As will become apparent from the description which follows, the present invention employs novel aminoalkyllithium compounds useful for example, as anionic polymerization initiators for the preparation of diene polymer and copolymer elastomers. It has been discovered herein that certain vulcanizable elastomeric compounds and articles thereof based upon such polymers formed using such initiators, exhibit useful properties, such as for example, reproducible relatively narrow molecular weight ranges. Furthermore, such polymers also contain a functionality from the initiator, which functionality is useful for example, in reducing hysteresis loss characteristics in the resulting polymers.
The preferred aminoalkyllithium compound used as anionic initiators in the invention contains a cyclic amine. The preferred initiator is therefore, an amine having the general formula ALi, wherein the component xe2x80x9cAxe2x80x9d represents the cyclic amine functionality to be incorporated at the initiation site or the head of the resulting polymer when the inventive amine compound is employed as an initiator. xe2x80x9cAxe2x80x9d is preferably a cyclic amine radical having the general formula (I) 
wherein R1 is a divalent alkylene, oxy- or amino-alkylene, or substituted alkylene moiety having from 6 to about 20 carbon atoms, more preferably from 6 to 12 carbon atoms; and, R2 is a linear-, branched-, or cyclo-alkylene moiety having from about 2 to about 20 carbon atoms, and more preferably, from 3 to 12 carbon atoms. The lithium atom, Li, is bonded directly to a carbon atom of A.
Examples of R1 include hexamethylene, heptamethylene, dodecamethylene and hexadecamethylene moieties and the like. Examples of preferred R2 groups have from about 3 to about 6 carbon atoms and include propyl and hexyl moieties and the like. Hence, examples of preferred cyclic amino compounds according to the invention include hexamethyleneiminopropyllithium, 
hexamethyleneiminohexyllithium, 
and, dodecamethyleneiminopropyllithium 
The carbon and nitrogen atoms in the cyclic amine ring structure of xe2x80x9cAxe2x80x9d can also be substituted, such that the aminoalkyllithium of this embodiment has the general formula 
wherein R3 is a tertiary amino or an alkyl group having from about 1 to about 12 carbon atoms; an aryl having from about 6 to about 20 carbon atoms; an aralkyl having from about 7 to about 20 carbon atoms; an alkenyl having from about 2 to about 12 carbon atoms; a cycloalkyl having from about 5 to about 20 carbon atoms; a cycloalkenyl having from about 5 to about 20 carbon atoms; a bicycloalkyl having from about 6 to about 20 carbon atoms; or, a bicycloalkenyl having from about 6 to about 20 carbon atoms; where n is an integer of from about 1 to about 10. The O-, S- or N-containing analogs of R3, which analogs are substantially non-reactive with the alkylithium of the cyclic amino compound, are also within the scope of the invention. By xe2x80x9canalogxe2x80x9d it is meant a compound in which one or more 0, S and/or N atoms may replace one or more carbon atoms. The lithium atom, Li, is bonded directly to a carbon atom in R2.
Further, R2 can be a branched- or cyclo-alkylene in addition to being a linear-alkylene as discussed hereinabove. Examples of branched-alkylene-containing (lithio)alkyl portions include 2,2-dimethylpropane-1,3-diyl; 2-methylpropane-1,3-diyl; 2-methylbutane-1,4 diyl; and 2-2-dimethyloctane-1,8-diyl. Examples of cyclo-alkylene (lithio)alkyl portions include cyclohexane-1,4-diyl; cyclohexane-1,3-diyl; cyclododecane-1,7-diyl; cyclooctane-1,3-diyl; and, cyclohexadecane-1,5-diyl.
According to another embodiment of the present invention, the cycloalkyl amine portion of xe2x80x9cAxe2x80x9d has at least seven ring atoms therein, including about 2 to about 4 amine nitrogens. Such a cyclic amine compound has the general formula R4R2Li where R2 is as defined above, and R4 is a cyclic amino radical having the general formula 
where R5 is selected from the group consisting of a divalent alkylene, an oxy- or amino-alkylene, and a substituted alkylene having from 4 to about 20 carbon atoms, a substituted nitrogen having the general formula R6N where R6 is selected from the group consisting of an alkyl having from 1 to about 12 carbon atoms; a cycloalkyl having from about 5 to about 20 carbon atoms; an aryl having from about 6 to about 20 carbon atoms; and, an aralkyl having from 7 to about 20 carbon atoms; and mixtures thereof, with the limitation that R4 has from 2 to about 4 nitrogen atoms and a total of from 6 to about 24 atoms in the ring structure thereof. The cyclic amine initiator according to the invention can thus have the following general formula, where R5, R2 and Li are as described hereinabove: 
The atoms in R5 can be substituted in the same manner as described above, that is, with xe2x80x9cAxe2x80x9d being substituted with (R3)n.
Therefore, in addition to formula (I) hereinabove, xe2x80x9cAxe2x80x9d can also be a cyclic amine radical having the general formula (II) R4R2xe2x80x94 where R4 and R2 are as described hereinabove.
Therefore, according to the present invention, in the alkyl lithium compounds containing cyclic amines, the size of the ring in the cyclic amine portion is greater than or equal to 7 atoms when there is only one nitrogen atom in the ring, or greater than or equal to 6 atoms when there are 2 or more nitrogen atoms in the ring.
Examples of amine compounds having the structure R4R2Li as above are mono-N alkyl or N-aryl derivatives or piperazines; mono N-alkyl derivatives of homopiperazine (1,4-diazacycloheptanes); mono-N-alkyl derivatives of 1,4- or 1,5-diazacyclooctanes, and ring C-substituted 1,4- or 1,5-diazacyclooctanes and the like. Ring C-substituted N-alkylpiperazines are also within the scope of the invention. Substituted triaza ring systems are also included within R4xe2x80x94.
The initiator used in the present invention can be formed by any number of techniques. One preferred method of preparing a cyclic amine compound according to the invention is to react a cyclic aminoalkyl halide with a lithio reactant selected from elemental lithium metal, an organolithium compound, and mixtures thereof. The aminoalkyl halide has the general formula AX where A is as defined by formulas I or II hereinabove, and X is a halogen selected from bromine, chlorine, iodine or the like, preferably bromine or chlorine, and wherein X is bonded directly to a carbon atom of R2 in either formula I or II. The preparation of cyclic aminoalkyl halides is known to the art.
When reacted with elemental lithium metal in a suitable solvent such as hexane, cyclohexane, benzene or the like, the resulting reduction reaction produces a lithiated cyclic amine compound ALi where xe2x80x9cAxe2x80x9d is as defined hereinabove and the lithium atom, Li, is directly bonded to a carbon atom of A. The lithiated cyclic amine compound ALi can be complexed with one or more ligand molecules (such as THF) which help stabilize it but do not otherwise affect the reaction.
In the alternative, the amino reactant AX can also be reacted with an organolithium reactant having the general formula RLi, again in a suitable solvent such as those described hereinabove. RLi can be for example, selected from the group consisting of alkyls, cycloalkyls, alkenyls, aryls and aralkyls having from 1 to about 20 carbon atoms and short chain length low molecular weight polymers from diolefin and vinyl aryl monomers having up to about 25 units. Typical alkyls include n-butyl, s-butyl, t-butyl, methyl, ethyl, isopropyl and the like. The cycloalkyls include cyclohexyl, menthyl and the like. The alkenyls include allyl, vinyl and the like. The aryl and aralkyl groups include phenyl, benzyl, oligo(styryl) and the like. Exemplary short chain length polymers include the oligo(butadienyls), oligo(isoprenyls), oligo(styryls) and the like. Alkyllithium reactants such as t-butyl lithium are preferred.
The two components are allowed to react for up to about twenty-four hours at low to ambient temperature (-70xc2x0 to 30xc2x0 C.), or elevated temperatures up to about 100xc2x0 C., preferably at less than 50xc2x0 C., and more preferably at less than 38xc2x0 C.
If one atom equivalent of lithium in the organolithium reactant is used per atom equivalent of AX, a byproduct of the reaction will be an organo halide (that is, RX) which may be undesirable for the intended use of the inventive compound. It may therefore, be preferable to employ two or more atom equivalents of lithium from the organolithium reactant per atom equivalent of AX. It is believed that a reaction with the excess of lithium will result in a lithium halide and other low molecular weight hydrocarbon by-products, which may be more acceptable for the intended use of the inventive initiator material.
As stated above, the compound ALi or R4R2Li thus formed may be employed as an initiator to prepare any anionically-polymerized elastomer, e.g., polybutadiene, polyisoprene and the like, and copolymers thereof with monovinyl aromatics such as styrene, alpha methyl styrene and the like, or trienes such as myrcene. Thus, the elastomers include diene homopolymers and copolymers thereof with monovinyl aromatic polymers. Suitable monomers include conjugated dienes having from about 4 to about 12 carbon atoms and monovinyl aromatic monomers having 8 to 18 carbon atoms and trienes. Examples of conjugated diene monomers and the like useful in the present invention include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene and 1,3-hexadiene, and aromatic vinyl monomers include styrene, alpha-methylstyrene, p-methylstyrene, vinyltoluene and vinylnaphthalene. The conjugated diene monomer and aromatic vinyl monomer are normally used at the weight ratios of 95-50:5-50, preferably 95-65:5-35.
Polymerization is conducted in polar or non-polar solvent, such as tetrahydrofuran (THF), a hydrocarbon solvent, such as the various cyclic and acyclic hexanes, heptanes, octanes, pentanes, their alkylated derivatives, and mixtures thereof. In order to promote randomization in copolymerization and to control vinyl content, a polar coordinator may be added to the polymerization ingredients. Amounts range between 0 and 90 or more equivalents per equivalent of lithium. The amount depends on the amount of vinyl desired, the level of styrene employed and the temperature of the polymerization, as well as the nature of the specific polar coordinator (modifier) employed. Suitable polymerization modifiers include for example, ethers or amines to provide the desired microstructure and randomization of the comonomer units. The molecular weight of the polymer (xe2x80x9cbase polymerxe2x80x9d) that is produced in this invention is optimally such that a proton-quenched sample will exhibit a gum Mooney (ML/4/100) of from about 1 to about 150. However, useful lower molecular weight compounds can also be made using these initiators. These might typically be considered fluids, having molecular weights ranging from several hundreds to tens of thousands of mass units.
Other compounds useful as polar coordinators are organic and include tetrahydrofuran (THF), linear and cyclic oligomeric oxolanyl alkanes such as 2,2-bis(2xe2x80x2-tetrahydrofuryl) propane, di-piperidyl ethane, dipiperidyl methane, hexamethylphosphoramide, N-Nxe2x80x2-dimethylpiperazine, diazabicyclooctane, dimethyl ether, diethyl ether, tributylamine and the like. The linear and cyclic oligomeric oxolanyl alkane modifiers are described in U.S. Pat. No. 4,429,091, owned by the Assignee of record, the subject matter of which relating to such modifiers is incorporated herein by reference. Compounds useful as polar coordinators include those having an oxygen or nitrogen hetero-atom and a non-bonded pair of electrons. Other examples include dialkyl ethers of mono and oligo alkylene glycols; xe2x80x9ccrownxe2x80x9d ethers; tertiary amines such as tetramethylethylene diamine (TMEDA); linear THF oligomers; and the like.
A batch polymerization is begun by charging a blend of monomer(s) and normal alkane solvent to a suitable reaction vessel, followed by the addition of the polar coordinator (if employed) and the initiator compound previously described. The reactants are heated to a temperature of from about 20 to about 200xc2x0 C., and the polymerization is allowed to proceed for from about 0.1 to about 24 hours. A functional amine group is derived from the initiator compound and attaches at the initiation site. Thus, substantially every resulting polymer molecule can be represented by the following general formula
AYLi
where A is as described above, and Y is a divalent polymer radical which is derived from any of the foregoing diene homopolymers, monovinyl aromatic polymers, diene/monovinyl aromatic random copolymers and block copolymers. The monomer addition at the lithium end causes the molecular weight of the polymer to increase as the polymerization continues.
To terminate the polymerization, and thus further control polymer molecular weight, a terminating agent, coupling agent or linking agent may be employed, all of these agents being collectively referred to herein as xe2x80x9cterminating reagentsxe2x80x9d. Certain of these reagents may provide the resulting polymer with a multifunctionality. That is, the polymers initiated according to the present invention, may carry at least one amine functional group A as discussed hereinabove, and may also carry a second functional group selected and derived from the group consisting of terminating reagents, coupling agents and linking agents.
Useful terminating, reagents include active hydrogen compounds such as water or alcohol; carbon dioxide; N,N,Nxe2x80x2,Nxe2x80x2-tetradialkyldiamino-benzophenone (such as tetramethyldiaminobenzophenone or the like); N,N-dialkylamino-benzaldehyde (such as dimethylaminobenzaldehyde or the like); 1,3-dialkyl-2-imidazolidinones (such as 1,3-dimethyl-2-imidazolidinone or the like); 1-alkyl substituted pyrrolidinones; 1-aryl substituted pyrrolidinones; dialkyl- and dicycloalkyl-carbodiimides having from about 5 to about 20 carbon atoms; (R7)aZXb; 
where Z is tin or silicon. It is preferred that Z is tin.
R7 is an alkyl having from about 1 to about 20 carbon atoms; a cycloalkyl having from about 3 to about 20 carbon atoms; an aryl having from about 6 to about 20 carbon atoms; or, an aralkyl having from about 7 to about 20 carbon atoms. For example, R7 may include methyl, ethyl, n-butyl, neophyl, phenyl, cyclohexyl or the like.
X is chlorine or bromine, xe2x80x9caxe2x80x9d is from 0 to 3, and xe2x80x9cbxe2x80x9d is from about 1 to 4; where a+b=4.
Each R8 is the same or different and is an alky, cycloalkyl or aryl, having from about 1 to about 12 carbon atoms. For example, R8 may include methyl, ethyl, nonyl, t-butyl, phenyl or the like.
R8 is an alkyl, phenyl, alkylphenyl or dialkylaminophenyl, having from about 1 to about 20 carbon atoms. For example, Rg may include t-butyl, 2-methyl-4-pentene-2-yl, phenyl, p-tolyl, p-butylphenyl, p-dodecylphenyl, p-diethyl-aminophenyl, p-(pyrrolidino)phenyl, and the like.
Each R10 is the same or different, and is an alkyl or cycloalkyl having from about 1 to about 12 carbon atoms. Two of the R10 groups may together form a cyclic group. For example, R10 may include methyl, ethyl, octyl, tetramethylene, pentamethylene, cyclohexyl or the like.
R11 may include alkyl, phenyl, alkylphenyl or dialkylaminophenyl, having from about 1 to about 20 carbon atoms. For example, R11 may include methyl, butyl, phenyl, p-butylphenyl, p-nonylphenyl, p-dimethylaminophenyl, p-diethylaminophenyl, p-(piperidino)phenyl, or the like.
Other examples of useful terminating reagents include tin tetrachloride, (R11)3SnCl, (R11)2SnCl2, R11SnCl3, carbodiimides, N-methylpyrrolidine, cyclic amides, cyclic ureas, isocyanates, Schiff bases, 4,4xe2x80x2-bis(diethylamino) benzophenone, and the like, where R11 is an alkyl, cycloalkyl or aralkyl having from 1 to about 12 carbon atoms, and other reactive hysteresis-reducing terminating compounds which may contain other heteroatoms such as oxygen, nitrogen, sulfur, phosphorus, tin, noninterfering halogen, etc. Suitable terminating reagents also include the isomeric vinylpyridines, dialkylaminobenzaldehydes, (bis) dialkylsminobenzophenones (Michler""s ketones), dimethylimidazolidinone, etc. The living polymer may also be coupled with any of the various known coupling reagents, such as silicon tetrachloride, etc., to prepare symmetrically xe2x80x9cdicappedxe2x80x9d polymers. By the end-linking of polymers initiated with lithium hydrocarbon amides, through reaction with for example, RaSnYb, where R, Y, a and b are as described hereinabove; SnCl4; or C4H9SnCl3; to obtain products with substantially greater than 10 percent end-linking through tin, especially desirable elastomeric compositions with low hysteresis properties are prepared.
The terminating reagent is added to the reaction vessel, and the vessel is agitated for about 1 to about 1000 minutes. As a result, an elastomer is produced having an even greater affinity for compounding materials such as carbon black, and hence, even further reduced hysteresis. Additional examples of terminating reagents include those found in U.S. Pat. No. 4,616,069 which is herein incorporated by reference for the disclosure of terminating agents.
The polymer may be separated from the solvent by conventional techniques. These include steam or alcohol coagulation, thermal desolventization, or any other suitable method. Additionally, solvent may be removed from the resulting polymer by drum drying, extruder drying, vacuum drying or the like.
The elastomers made from the anionic initiators of the present invention comprise a plurality of polymer molecules, having a functional group at both the head, and preferably also, at the tail of the resulting polymer. Compounding such elastomers results in products exhibiting reduced hysteresis, which means a product having increased rebound, decreased rolling resistance and has less heat build-up when subjected to mechanical stress.
The polymers made from the anionic initiators of the present invention can be used alone or in combination with other elastomers to prepare a product such as a tire treadstock, sidewall stock or other tire component stock compound. Such stocks are useful for forming tire components such as treads, subtreads, black sidewalls, body ply skims, bead fillers and the like. At least one such component is produced from a vulcanizable elastomeric or rubber composition. For example, they can be blended with any conventionally employed treadstock rubber which includes natural rubber, synthetic rubber and blends thereof. Such rubbers are well known to those skilled in the art and include synthetic polyisoprene rubber, styrene/butadiene rubber (SBR), polybutadiene, butyl rubber, poly(chloroprene), ethylene/propylene rubber, ethylene/propylene/diene rubber (EPDM), acrylonitrile/butadiene rubber (NBR), silicone rubber, the fluoroelastomers, ethylene acrylic rubber, ethylene vinyl acetate copolymer (EVA), epichlorohydrin rubbers, chlorinated polyethylene rubbers, chlorosulfonated polyethylene rubbers, hydrogenated nitrile rubber, tetrafluoroethylene/propylene rubber and the like. When the polymers of the present invention are blended with conventional rubbers, the amounts can vary widely such as between 10 and 99 percent by weight.
The polymers can be compounded with carbon black in amounts ranging from about 20 to about 100 parts by weight, per 100 parts of rubber (phr), with about 40 to about 70 phr being preferred. The carbon blacks may include any of the commonly available, commercially-produced carbon blacks but those having a surface area (EMSA) of at least 20 m2/g and more preferably at least 35 m2/g up to 200 m2/g or higher are preferred. Surface area values used in this application are those determined by ASTM test D-1765 using the cetyltrimethyl-ammonium bromide (CTAB) technique. Among the useful carbon blacks are furnace black, channel blacks and lamp blacks. More specifically, examples of the carbon blacks include super abrasion furnace (SAF) blacks, high abrasion furnace (HAF) blacks, fast extrusion furnace (FEF) blacks, fine furnace (FF) blacks, intermediate super abrasion furnace (ISAF) blacks, semi-reinforcing furnace (SRF) blacks, medium processing channel blacks, hard processing channel blacks and conducting channel blacks. Other carbon blacks which may be utilized include acetylene blacks. Mixtures of two or more of the above blacks can be used in preparing the carbon black products of the invention. Typical values for surface areas of usable carbon blacks are summarized in the following TABLE I.
The carbon blacks utilized in the preparation of the rubber compounds used may be in pelletized form or an unpelletized flocculent mass. Preferably, for more uniform mixing, unpelletized carbon black is preferred. The reinforced rubber compounds can be cured in a conventional manner with known vulcanizing agents at about 0.5 to about 4 phr. For example, sulfur or peroxide-based curing systems may be employed. For a general disclosure of suitable vulcanizing agents one can refer to Kirk-Othmer, Encyclopedia of Chemical Technolog, 3rd ed., Wiley Interscience, N.Y. 1982, Vol. 20, pp. 365-468, particularly xe2x80x9cVulcanization Agents and Auxiliary Materialsxe2x80x9d pp.390-402. Vulcanizing agents may be used alone or in combination.
Vulcanizable elastomeric compositions made from the above elastomers can be prepared by compounding or mixing the polymers thereof with carbon black and other conventional rubber additives such as fillers, plasticizers, antioxidants, curing agents and the like, using standard rubber mixing equipment and procedures and conventional amounts of such additives.
In order to demonstrate the preparation and properties of the initiators according to the present invention and their use in anionic polymerization, a number of such cyclic amino alkyllithium compounds were prepared. These compounds were then used as initiators to form a number of elastomers.
The aminoalkyllithium reagents of the invention may be prepared under a variety of conditions, using various hydrocarbon solvents as discussed hereinabove. The reagents may be used in polymerizations using such polar or nonpolar solvents as may be necessary for improved solubility of the aminoalkyllithium reagent, provided that the solvents are compatible with anionic polymerizations and the solvent recovery and polymer drying procedures.
In one preferred embodiment of the invention that provides for the production of reduced hysteresis polymers in substantially hydrocarbon solvents, such as hexane or cyclohexane, the initiator is hexamethyleneiminopropyllithium, which may be generated by at least two exemplary routes as is also discussed above: 1) by the reaction of a mixture of one equivalent of for example, 1-(N-hexamethyleneimino)-3-chloropropane with about two atom equivalents of lithium metal; or 2) a xe2x80x9cone-potxe2x80x9d generation of for example, hexamethyleneiminopropyllithium, wherein 1-bromo-3-chloropropane is treated with N-lithiohexamethyleneimine, and the product 1-(N-hexamethyleneimino)-3-chloropropane is then treated in situ with two equivalents of t-butyllithium. The reactions are preferably performed in hexanes, cyclohexane, benzene, or mixtures thereof.
The amino alkyllithium reagents of the invention may be formed in a solvent or solvent mixture, and then transferred to another solvent or solvent mixture for use in a polymerization reaction.
The initiators of this invention may optionally be treated with from about one to 500 equivalents of a monomer such as butadiene or isoprene, before the main (co)polymerization charge is made, although this is not required. Polymers according to the invention can be prepared with a relatively narrow molecular weight range distribution, with a substantial fraction of living Cxe2x80x94Li chain ends adaptable to further functionalization or coupling, being obtained.
The initiator formation, polymerization, and coupling and/or termination may be performed in one reaction vessel, or second or third reactor vessels, or transfer lines from the original reactor can be used, by introducing the preformed initiator to the monomer mixture, or vice-versa. Polymerization and post-treatment conditions should be used that avoid the introduction of air and/or protic or other reactive contaminants, such as moisture, etc., and prolonged heating or storage at excessive temperatures should be avoided unless the live ends are stabilized. Low to high temperatures (from about xe2x88x9270xc2x0 C. to about 200 xc2x0 C.) are useful for the polymerizations and the terminations. Polymerization and post-treatment temperatures of from about 15xc2x0 C. to 125xc2x0 C. are preferred. The polymerization time may vary from a few minutes to days, depending on the temperature, solvent and presence of any donor solvent, the monomer structures, and the molecular weight desired.
Any suitable method for isolation of the terminated rubber or fluid may be used, for example: quenching with water, steam, an acid or an alcohol (these may be introduced during the desolventization step), and desolventization by drum drying, coagulation in alcohol, water or steam, extruder drying, vacuum drying, spray drying or any combination thereof. Desolventization by drum-drying, coagulation in alcohol, steam or hot water desolventization, extruder drying, vacuum drying, spray drying or combinations thereof are preferred. An antioxidant and/or antiozonant compound is usually added to the polymer or polymer cement at or before this stage. In most of the experimental examples of this invention, alcohol coagulation followed by drum-drying or vacuum drying were used.
Upon drying, the elastomers are compounded in a carbon black-filled test stock (see Low-Oil Test Recipe, TABLE II), and the physical properties determined in comparison to those of related base polymers without the modifications. In practice, a wide variety of compounding recipes may be used to give favorable results with this invention, although hysteresis properties may vary from formulation to formulation, depending on the type and amount of carbon black and oil used, and so on. Certain other fillers, such as silica or hydrated silica may also be useful. Furthermore, the polymers made with the initiators of this invention may be combined in proportions of 20 to 100 percent by weight with 80 to 0 percent by weight of other polymers to give elastomeric compositions with reduced hysteresis loss characteristics. The low molecular weight products made from the initiators of this invention may be used at low levels to influence the properties of mixtures with other fluids and/or particulates.